There is a sharp increase in incident depression in adolescence, suggesting that this is a sensitive period of development. Adolescence is characterized by strong emotional reactivity; the hypothesized neural correlates of these behaviors include the functioning of frontolimbic (i.e. prefrontal cortex and amygdala) circuitry. However, less is known about the development of frontolimbic circuitry during adolescence itself, or about characteristics of the social environment that may promote emotion regulation during this sensitive period. In the proposed NIMH Mentored Research Scientist Development Award (K01), I draw on an epidemiological approach, neuroscience models of brain development and social and psychological theory to describe how social engagement may influence the development of emotion regulation and depressive symptoms during adolescence. I suggest that monitored social engagement(MSE), defined here as social interactions that are monitored by adults and guided by social norms in which there is an expectation of appropriate behavior, promotes the practice of emotion regulation and is a potential target for preventive interventions. I combine hypothesis testing and measurement development to further test this hypothesis. I propose to 1) use secondary data to test relationships between indicators of MSE and depressive symptoms in the National Longitudinal Survey of Adolescents (Add Health), 2) develop and administer a measure of MSE in a cohort of early and middle adolescents, and 3) use this cohort to examine age-related differences in frontolimbic connectivity, as well as relationships between frontolimbic connectivity, depressive symptoms and MSE. This research plan will be buttressed by a rigorous training plan that builds on my background in social epidemiology and foundational knowledge of neuroscience and neuroimaging, and includes developing 1) a deep understanding of the neurobiology of emotion regulation, depression and adolescent brain development, and 2) a greater understanding and facility with the design and analysis of more complex neuroimaging tasks, including functional connectivity analysis. To accomplish these training goals, I have assembled an expert, interdisciplinary mentorship team centered at the University of California San Francisco, which includes experts in adolescent affective neuroscience, clinical depression, measurement development, and neuroimaging. Training activities include didactic coursework, workshops, and ongoing supervision, and consultation with my mentorship team. The proposed training and research activities are designed to provide the additional experience and resources necessary to support my transition to independence and the submission of a successful R01 grant by the end of the award. I expect to propose a longitudinal cohort study of 10-11 year olds and examine the development of emotion regulation, frontolimbic circuitry, and depressive symptoms longitudinally, as well as the possible influence of monitored social engagement.